#include <bits/stdc++.h>
using namespace std;
#define int long long
#define fi first
#define se second
#define pii pair<int,int>
#define all(a) a.begin(), a.end()
#define el '\n'
const int maxN = 4005;
const int base = 311;
const int MOD = 1e9+7;
const int INF = 1e18;
const int NEG_INF = -1e18;
const int MAX_DAYS = 1000;
int dy[] = {-1, 1, 0, 0};
int dx[] = {0, 0, -1, 1};
int n, m, k, q, x;
string S, T;
int dist[maxN][maxN], par[maxN];
bool visited[maxN][maxN];
vector<int> g[maxN];
string grid[maxN];
// void bfs(int s){
// fill_n(dist, n + 1, -1);
// fill_n(visited, n + 1, false);
// fill_n(par, n + 1, -1);
// queue<int> q;
// q.push(s);
// visited[s] = true;
// dist[s] = 1;
// while(!q.empty()){
// int u = q.front();
// q.pop();
// for(auto v : g[u]){
// if(!visited[v]){
// dist[v] = dist[u] + 1;
// par[v] = u;
// visited[v] = true;
// q.push(v);
// }
// }
// }
// }
bool inside(int x, int y) {
return (x > 0 && x <= n && y > 0 && y <= m && grid[x][y] != '.');
}
int bfs_01() {
int ans = 1;
for(int i = 1; i <= n; i++){
for(int j = 1; j <= m; j++){
dist[i][j] = INF;
}
}
deque<pii> q;
q.push_front({1,1});
dist[1][1] = 1;
while(!q.empty()){
auto[x,y] = q.front();
q.pop_front();
ans = max(ans, dist[x][y]);
for(int k = 0; k < 4; k++){
int nxt_x = x + dx[k], nxt_y = y + dy[k];
if(!inside(nxt_x, nxt_y)) continue;
int w = (grid[x][y] == grid[nxt_x][nxt_y]) ? 0 : 1;
if(dist[nxt_x][nxt_y] > dist[x][y] + w){
dist[nxt_x][nxt_y] = dist[x][y] + w;
if(w == 1) q.push_back({nxt_x, nxt_y});
else q.push_front({nxt_x, nxt_y});
}
}
}
return ans;
}
// void Trace(int u){
// vector<int> path;
// while(u > 0){
// path.push_back(u);
// u = par[u];
// }
// reverse(path.begin(), path.end());
// for(int u : path) cout << u << " ";
// }
void run_test() {
cin >> n >> m;
for(int i = 1; i <= n; i++){
string s;
cin >> s;
s = '_' + s;
grid[i] = s;
}
cout << bfs_01() << endl;
}
signed main(){
ios::sync_with_stdio(false);
cin.tie(nullptr);
// freopen("pieaters.in", "r", stdin);
// freopen("pieaters.out", "w", stdout);
int test = 1;
// cin >> test;
while (test-- > 0)
{
run_test();
}
}
